Application of heat therapy, cold therapy (cryotherapy), and contrast therapy (alternating heat and cold therapy) is used to treat a multitude of conditions including muscle and joint pain, strains, sprains, a variety of arthritic conditions, menstrual cramps, and a variety of other maladies. The earliest applications of heat therapy used hot towels or hot stones wrapped in towels. Electric heating pads, clay filled packs kept in hot water tanks, gel packs, alumina and grain packs heated in the microwaves, hot water bottles, water recirculation systems, and paraffin baths have been the methods available to application of heat therapy.
Application of cold therapy has been done using ice bags, gel packs, and water recirculation systems. In each of the methods of application, a heat or cold pack is directly applied to the body for the treatment time of typically 20 to 30 minutes. In some cases, ties or elastic straps have been provided to affix the treatment pack to the body, but in many cases the pack simply rests on the targeted area.
Commercially available hot and cold packs use various thermally conductive solutions and suspensions to provide heat (cold) transfer in hot and cold therapy packs. All of these products use water, glycols, glycerin, or other organic liquids as one of their principal components. They utilize a variety of thickening agents that are designed to increase the viscosity of the fluid and reduce its naturally occurring free flowing characteristics.
A significant shortcoming of currently available technologies is that they do not provide for consistent delivery of hot or cold therapy. Most commonly used hot and cold packs use some form of liquid or gel as the medium that stores heat or cold to be transferred to the body on application. Because the liquid/gel is free flowing within the containing envelope, there is an uneven distribution of the liquid/gel within the pack and saddle-bagging in the region of application is a common complaint. This saddle-bagging results in uneven distribution of heat (or cold) and a less than optimum outcome of the modality. This is specially true for application to body parts of small cross-section (fingers, wrists, etc.), application to children, and veterinary applications to small animals. Addition of thickening and gelling agents is not sufficient to overcome this limitation. Excessive amounts of gelling/thickening agents into the mixture result in a semi-solid hot/cold pack that may become brittle and fracture when cold. The contents may break into smaller, non-uniform pieces which remain discrete and do not return to a single mass. Furthermore, increasing the gel viscosity can be costly and ineffective.
Addition of traditional low density open cell or closed cell (sponge) foams does not address the poor performance of existing hot/cold packs either. Use of closed cell is not effective because the liquid/gel formulations cannot occupy the void spaces present in the foam. Its use gives the impression of mass and improved liquid/gel distribution, but in no way reduces the saddle-bagging because the material voids are isolated from the liquid or gel. The liquid still saddle-bags and the foam only gives the illusion of benefit.
Use of open cell foams (sponge) necessitates selection of low viscosity fluids (water, etc) that can readily flow into the open cells. High viscosity formulations cannot enter the voids. In the low viscosity version, fluids flow into and out of the through the cells and pool outside the foam. Presence of the foam again creates the illusion of benefit, does not restrict the flow of the liquid. Efforts to utilize more viscous gels and open celled foams have not been satisfactory because air becomes trapped within the pack resulting in significant loss of efficacy. Because the thicker gels cannot penetrate into the void space easily, saddle-bagging continues to be manifested during application. Once other side effect is that the air can later release into the bag resulting in pillowing of the gel packs. This pillowing is further detrimental to the optimum application of heat or cold.
Optimum heat transfer (or cold transfer) occurs when there is good physical contact between the hot/cold pack and the skin. Additionally, uniform heat transfer is made possible by both good physical contact between the surfaces and uniform distribution of the liquid/gel in the cold pack, even when applied to small limbs and in a vertical orientation. It is the vertical orientation, coupled with low viscosity fluids and ineffective designs that amplifies the undesirable saddle-bagging.